Considerable effort has been given to improving fuel consumption in automobiles. The principal avenues for achieving improvement are through reduced vehicle weight, improved combustion process, reduced aerodynamic drag, reduced wheel rolling friction, and reduced engine friction. Engine friction can be present where moving parts are in engagement, the principal ones being the valve operating train with a variety of contacts through sleeve and stem interengagements, rocker arm pivoting, and camshaft engagement of tappets, all of which attempt to convert the rotary motion of a camshaft into the linear motion of the valve stem.
Due to efforts to improve fuel efficiency through methods other than reduced friction, the sum total of engine friction has been somewhat increased in recently designed engines. For example, in engines employing the hemi-head cylinder construction, the rearrangement of the intake and exhaust valves about a spherical surface causes the valve axes to be oriented in unusual patterns. The use of skewed rocker arms operating about a single overhead camshaft promotes side loading forces which results in increased friction. The valve stem is embraced by a spring effective to exert a closing force on the valve, the valve opening being accomplished by the rocker arm overcoming such spring. The spring force is always high to accommodate operating at high speeds. Much greater spring forces are required to provide sufficient closing force to overcome the inertia of the valve. With the necessity for such heavier springs and the accompanying additional side loading frictional forces, the engine friction force, at medium to low load conditions, is undersirably high.
Prior attempts have been made to vary the closing force of the internal combustion engine valves by use of a variable fulcrum (see U.S. Pat. No. 4,134,371), by varying the stroke adjustment of the valve operating train (see U.S. Pat. No. 4,187,810), and by selectively using hydraulics to assist the spring closing force (see U.S. Pat. No. 2,342,003). However, all of these patents fail to affect the original design of the spring element used for the closing force at low speed conditions. The springs in these patents, being designed primarily for high speed conditions, are also operative at the low speed conditions without change even though the valve leverage system may be adjusted upstream from the spring. Thus there is no net reduction in engine friction as a result of such valve train adjustment.
Several prior art approaches have been made in an effort to augment the spring force under high speed conditions such as by use of pressurized hydraulic fluid to add to the spring force (see U.S. Pat. No. 2,342,003).
Another area for high friction is the drive system used to interconnect the engine crankshaft with various driven components such as the camshaft and water pump. Belts, designed to have a serpentine path, engage more than one driven pulley, requiring an idler pulley to maintain tension in the belt and ensure satisfactory timing and drive of the driven members. Considerable friction is imparted as a result of applying sufficient tension to a belt with such a path. In conditions where engine vibration permits, it is desirable if the belt tension can be removed so as to release some side loading on the bearing of the driven members as well as input members. Prior art devices have attempted to vary the belt tension on idler pulleys, such as in U.S. Pat. Nos. 3,496,918; 3,888,217; and 4,077,272. In each of these patents, side loading of the pulleys receiving drive were not relieved of friction by moving the idler pulley; instead, side loading was increased by angulating the idler pulley support with respect to the belt path in an attempt to vary the valve timing, thereby lengthening one side of the belt train as opposed to the other side and thus changing the valve timing. These devices have had little effect upon changing the belt friction forces operating on the bearings and therefore are ineffective in reducing engine friction, particularly during high speed operating conditions.